U.S. patent number 6,686,274 [Application Number 09/787,743] was granted by the patent office on 2004-02-03 for semiconductor device having cobalt silicide film in which diffusion of cobalt atoms is inhibited and its production process.
This patent grant is currently assigned to Renesas Technology Corporation. Invention is credited to Shuji Ikeda, Tomio Iwasaki, Hideo Miura, Hiroyuki Ohta, Hiromi Shimazu.
United States Patent |
6,686,274 |
Shimazu , et al. |
February 3, 2004 |
Semiconductor device having cobalt silicide film in which diffusion
of cobalt atoms is inhibited and its production process
Abstract
In a semiconductor device having a cobalt silicide film, at
least nickel or iron is contained in the cobalt silicide film for
preventing the rise of resistance incidental to thinning of the
film.
Inventors: |
Shimazu; Hiromi (Tsuchiura,
JP), Iwasaki; Tomio (Tsuchiura, JP), Ohta;
Hiroyuki (Tsuchiura, JP), Miura; Hideo
(Tsuchiura, JP), Ikeda; Shuji (Kodaira,
JP) |
Assignee: |
Renesas Technology Corporation
(Tokyo, JP)
|
Family
ID: |
17448263 |
Appl.
No.: |
09/787,743 |
Filed: |
June 8, 2001 |
PCT
Filed: |
September 20, 1999 |
PCT No.: |
PCT/JP99/05108 |
PCT
Pub. No.: |
WO00/17939 |
PCT
Pub. Date: |
March 30, 2000 |
Foreign Application Priority Data
|
|
|
|
|
Sep 22, 1998 [JP] |
|
|
10/267695 |
|
Current U.S.
Class: |
438/653;
257/E21.165; 257/E21.585; 257/E21.438; 438/655 |
Current CPC
Class: |
H01L
29/665 (20130101); H01L 21/28518 (20130101); H01L
21/76877 (20130101) |
Current International
Class: |
H01L
21/285 (20060101); H01L 21/768 (20060101); H01L
21/02 (20060101); H01L 21/70 (20060101); H01L
21/336 (20060101); H01L 021/44 () |
Field of
Search: |
;438/653
;757/766,757,755,758,769 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Mo et al., "Formation and Properties of ternary silicide (CoNi)Si2
thin films", IEEE, 1998 5.sup.th International Conference on Solid
State and Integrated Circuit Technology, pp 271-274.* .
Hong et al., Magneto-optic Kerr effect measurements on FeCoSi
epitaxially stabilized on Si (111), Journal of Magetism and
Magnetic Materials, vol. 165, pp 212-215.* .
http://www.puretechinc.com and
http://www.tosohsmd.com/tsprod/tspcobdt.htm, Material Data Sheet
MDS 27.000 which includes the total metallics of the cobalt
target., pp. 1-4 and pp. 1-3.* .
Safety & Health Guide for the Microelectronics Industry,
"Hazard Communication", OSHA 3107, pp 9, 1998..
|
Primary Examiner: Coleman; W. David
Attorney, Agent or Firm: Antonelli, Terry, Stout &
Kraus, LLP
Claims
What is claimed is:
1. A semiconductor device comprising: a silicon substrate; a
silicon-made gate electrode formed on said silicon substrate; a
diffusion layer(s) formed close to said gate electrode; and a
cobalt silicide film formed on at least said gate electrode or said
diffusion layer, wherein at least nickel or iron is contained in
said cobalt silicide film in an amount of 0.05 to 50 atomic %.
2. A semiconductor device according to claim 1, wherein the ratio
of nickel or iron to cobalt in the cobalt silicide film is 0.05 to
18 atomic %.
3. A semiconductor device comprising: a silicon substrate having
MOS transistors formed thereon; an insulating film formed on said
silicon substrate; contact holes formed in said insulating film; a
polycrystalline silicon plug provided in each of said contact
holes; metal wiring provided on said insulating film; and a cobalt
silicide film formed at least at the interface between said metal
wiring and said polycrystaline plug or at the interface between
said metal wiring and said silicon substrate, wherein at least
nickel or iron is contained in said cobalt silicide film in an
amount of 0.05 to 50 atomic %.
4. A semiconductor device comprising: a silicon substrate having
MOS transistors formed thereon; an insulating film formed on said
silicon substrate; contact holes formed in said insulating film; a
polycrystalline silicon plug provided in each of said contact
holes; metal wiring provided on said insulating film; and a cobalt
silicide film formed at least at the interface between said metal
wiring and said polycrystalline plug, at the interface between said
metal wiring and said silicon substrate or at the interface between
said metal wiring and the gate electrode of each of said MOS
transistors, wherein at least nickel or iron is contained in said
cobalt silicide film in an amount of 0.05 to 50 atomic %.
5. A semiconductor device comprising: a silicon substrate having
MOS transistors formed thereon; an insulating film formed on said
silicon substrate; a capacitor provided on said insulating film;
and a cobalt silicide film formed at least on the gate electrode of
each of said MOS transistors, wherein at least nickel or iron is
contained in said cobalt silicide film in an amount of 0.05 to 50
atomic %.
6. A process for producing a semiconductor device comprising the
steps of: forming a gate electrode on a silicon substrate; forming
a diffusion layer(s) on said silicon substrate; forming a cobalt
film in contact with the upper side of at least said gate electrode
or said diffusion layer(s); depositing at least a nickel film or an
iron film on said cobalt film; and forming a cobalt silicide film
containing at least nickel or iron in an amount of 0.05 to 50
atomic % on at least said gate electrode or said diffusion
layer(s).
7. A process for producing a semiconductor device comprising the
steps of: forming a gate electrode on a silicon substrate; forming
a diffusion layer(s) on said silicon substrate; depositing a cobalt
film containing at least nickel or iron on at least said gate
electrode or diffusion layer(s); and forming a cobalt suicide film
containing at least nickel or iron in an amount of 0.05 to 50
atomic % on at least said gate electrode or said diffusion
layer(s).
8. The process according to claim 7, wherein said cobalt film
containing at least nickel or iron is deposited by multi-stage
sputtering.
9. The process according to claim 7, wherein said cobalt film
containing at least nickel or iron is deposited by sputtering using
a cobalt target containing at least nickel or iron.
10. A process for producing a semiconductor device comprising the
steps of: forming an insulating film on a silicon substrate having
MOS transistors formed thereon; providing contact holes in said
insulating film; forming a cobalt film in each of said contact
holes; forming at least a nickel film or an iron film on said
cobalt film; and forming a cobalt silicide film in each of said
contact holes by a heat treatment.
11. A process for producing a semiconductor device comprising the
steps of: forming an insulating film on a silicon substrate having
MOS transistors formed thereon; providing contact holes in said
insulating film; forming a polycrystalline silicon plug in each of
said contact holes; forming a cobalt film on said polycrystalline
silicon plug in each of said contact holes; forming at least a
nickel film or an iron film on said cobalt film; and forming a
cobalt silicide film containing at least nickel or iron in an
amount of 0.05 to 50 atomic % in each of said contacts hole by a
heat treatment.
12. A process for producing a semiconductor device comprising the
steps of: forming an insulating film on a silicon substrate having
MOS transistors formed thereon; providing contact holes in said
insulating film; forming a cobalt film containing at least nickel
or iron in each of said contact holes; and forming a cobalt
silicide film in each of said contacts hole by a heat
treatment.
13. A process for producing a semiconductor device comprising the
steps of: forming an insulating film on a silicon substrate having
MOS transistors formed thereon; providing contact holes in said
insulating film; forming a polycrystalline silicon plug in each of
said contact holes; forming a cobalt film containing at least
nickel or iron on said polycrystalline silicon plug in each of said
contact holes; and forming a cobalt silicide film containing at
least nickel or iron in an amount of 0.05 to 50 atomic % in each of
said contact holes by a heat treatment.
Description
TECHNICAL FIELD
The present invention relates to a semiconductor device and its
production process, particularly to a semiconductor device having a
cobalt silicide film and its production process.
BACKGROUND ART
With the recent trend toward higher integration and miniaturization
of the semiconductor devices, reduction of contact resistance at
the joint of metal wiring and silicon substrate has become
essential for high-speed operation. Regarding the techniques for
reducing contact resistance, for instance JP-A-08-78357 suggests to
form a cobalt silicide film on the diffusion layer (source/drain)
or polycrystalline silicon electrodes on a silicon substrate.
DISCLOSURE OF THE INVENTION
However, when the diffusion layer is made shallow and the cobalt
silicide film is thinned with miniaturization of the semiconductor
devices, there arises the new problem that the cobalt silicide
coating, which was film-like when formed, is coagulated by a
high-temperature heat treatment in, for instance, the capacitor
forming step and takes a partially insular configuration, causing a
rise of resistance.
The object of the present invention is to solve the above problem
and provide a semiconductor device having a cobalt silicide film
which is proof against coagulation and remains low in resistance
even if reduced in thickness, and a process for producing such a
semiconductor device.
Rise of resistance of the cobalt silicide film is attributable to
the insular coagulation of the cobalt silicide which occurs when
the cobalt (Co) atoms composing the cobalt silicide film are
diffused mostly along the crystal grain boundaries and recombined
with silicon in a heat treatment at around 800.degree. C. or above.
Therefore, for preventing the rise of resistance due to the
coagulation of cobalt silicide film, it is expedient to inhibit the
diffusion of cobalt atoms in the cobalt silicide film.
On this concept, the present inventors disclosed that it is
possible to inhibit the grain boundary diffusion of Co atoms in the
cobalt silicide film when a specific element--an element having a
smaller atomic radius than Co atom and specified by the fact that
the inter-hetero-atomic energy between this element and Co element
is not more than 20% smaller or greater than the inter-iso-atomic
energy of Co element--is contained in said cobalt silicide film.
That is, it was found the diffusion of Co atoms can be inhibited by
containing nickel or iron element in the cobalt silicide film, and
that in this case, the ratio of nickel or iron element to cobalt in
said film should be preferably 0.05 to 50 atomic %, more preferably
0.05 to 18 atomic %.
It was also found that the use of multi-stage sputtering or an
alloy target is suited for forming the said cobalt silicide
film.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of a principal part of a semiconductor
device in a first embodiment of the present invention.
FIG. 2 is a diagrammatic illustration of the effect of inhibiting
the grain boundary diffusion of cobalt atoms in a cobalt silicide
film by containing an adding element in said film.
FIG. 3 is a sectional view showing the state of segregation of Ni
at the crystal grain boundaries in an Ni-containing cobalt silicide
film.
FIG. 4 is a sectional view of a principal part of a semiconductor
device in a second embodiment of the present invention.
FIG. 5 is a sectional view of a principal part of a semiconductor
device in a third embodiment of the present invention.
FIG. 6 is a sectional view of a principal part of a semiconductor
device in a fourth embodiment of the present invention.
FIG. 7 is an illustration showing part of the production process of
a semiconductor device in a fifth embodiment of the present
invention.
FIG. 8 is an illustration showing part of the production process of
the semiconductor device in the fifth embodiment of the present
invention.
FIG. 9 is an illustration showing part of the production process of
the semiconductor device in the fifth embodiment of the present
invention.
FIG. 10 is an illustration showing part of the production process
of the semiconductor device in the fifth embodiment of the present
invention.
FIG. 11 is an illustration showing a characteristic feature in
shape of the cobalt silicide film formed by the production process
of the semiconductor device in the fifth embodiment of the present
invention.
FIG. 12 is an illustration showing part of the production process
of a semiconductor device in a sixth embodiment of the present
invention.
FIG. 13 is an illustration showing part of the production process
of the semiconductor device in the sixth embodiment of the present
invention.
FIG. 14 is an illustration showing part of the production process
of the semiconductor device in the sixth embodiment of the present
invention.
FIG. 15 is an illustration showing part of the production process
of the semiconductor device in the sixth embodiment of the present
invention.
FIG. 16 is a graph showing the influence of the adding element
concentration on the grain boundary diffusion coefficient when an
adding element was added in an amount of 0 to 0.3 atomic % in a
cobalt silicide film.
FIG. 17 is a graph showing the influence of the adding element
concentration on the grain boundary diffusion coefficient when the
adding element was added in an amount of 5 to 20 atomic % in the
cobalt silicide film.
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described regarding its
embodiments with reference to the accompanying drawings.
First, a sectional structure of a principal part of a semiconductor
device in a first embodiment of the present invention is shown in
FIG. 1.
The semiconductor device according to this embodiment of the
invention, as shown in FIG. 1, has MOS transistors 100 formed on
the surface of a silicon substrate, each of said MOS transistors
comprising a gate oxide film 3, a gate electrode 4 made of a
polycrystalline silicon film, and a pair of diffusion layers 5, 6
(source and drain region). These MOS transistors are isolated by
the isolating films 2. Said gate electrode 4 is made of a
polycrystalline silicon film, a thin metal film, a metal silicide
film or a laminate thereof. Side walls 7 are formed on both sides
of said gate electrode 4. The gate oxide film 3 is made of, for
instance, a silicon oxide,film, a silicon nitride film, a
ferroelectric film or a laminate thereof.
Cobalt silicide films 8, 9, 10 are formed on the gate electrode 4
and the diffusion layers 5, 6. Said cobalt silicide films 8, 9, 10
contain at least one adding element, and at least one of such
adding elements is nickel (Ni) or iron (Fe).
The Ni or Fe atoms in said cobalt silicide films 8, 9, 10 may exist
either in the form of nickel or iron silicide or as a single body
of Ni or Fe.
The gate electrode 4 and diffusion layers 5, 6 on which said cobalt
silicide films 8, 9, 10 are formed, and the electrical wirings 16,
17 of the first layer are electrically connected in the contact
holes 13, 14 formed in an insulating film 12 of the first layer.
Further, over the top of said first layer windings 16, 17 is
provided an insulating film 19 for electrically insulating the unit
from the outside. Said insulating film 19 may be made of, for
instance, a BPSG (boron-doped phosphosilicate glass) film, a SOG
(spin-on-glass) film or a silicon oxide or nitride film formed by
CVD or sputtering.
Next, the action and effect of the semiconductor device according
to the instant embodiment of the invention is described. The
conventional cobalt silicide film would be elevated in resistance
by a heat treatment of about 700.degree. C. or higher after
formation of the film. This is attributable to the coagulation of
cobalt silicide which occurs as the Co atoms composing the cobalt
silicide film are diffused along the crystal grain boundaries of
cobalt silicide and move toward the chemically more stable Si atoms
to recombine with them when the film is heat treated at around
700.degree. C. or above in a step after formation of the film.
Therefore, inhibition of the grain boundary diffusion of Co atoms
is a positive way for preventing elevation of resistance due to
agglomeration of the cobalt silicide film.
Iron has the advantage of allowing reduction of stress of the
silicide film with ease, while nickel is advantageous in that it
has the effect of making the film hard to oxide.
The present inventors found that it is possible to inhibit the
grain boundary diffusion of Co atoms in the cobalt silicide film by
containing a specific adding element in the film.
FIG. 2 shows the effect of inhibiting the grain boundary diffusion
of cobalt atoms in a cobalt silicide film by containing an adding
element in the film. Such inhibitory effect of the adding element
is represented by the rate of decrease of grain boundary diffusion
coefficient.
In FIG. 2, the grain boundary diffusion coefficient D of Co atoms
in a cobalt silicide film was calculated by calculator simulation,
and the effect of the adding element is shown diagrammatically by
focusing attention on the atomic radius and bond energy of the
adding element. In this embodiment, each adding element was
contained in an amount of 0.2 atomic %, and D.sub.0 denotes the
grain boundary diffusion coefficient when no adding element was
contained. Calculator simulation used here is molecular dynamic
simulation. Molecular dynamic simulation is a method in which, as
for instance explained in Journal of Applied Physics, Vol. 53
(1983), pages 4864-4878, the force working between the atoms
through interatomic potential is calculated, and based on this
force, the Newton's equation of motion is solved to determine the
position of each atom at each time. The method of calculating the
diffusion coefficient by molecular dynamic simulation is shown in,
for instance, Physical Review B, Vol. 29 (1984), pages 5363-5371.
Here, the effect of the adding elements was described by taking up
the case where the diffusion coefficient of Co atoms at the crystal
grain boundaries was calculated by setting the temperature at 1,000
K. This effect can be explained in the same way even when the
simulation conditions are changed.
It was found from FIG. 2 that it is possible to minimize the grain
boundary diffusion coefficient D when the adding element has a
smaller atomic radius than the Co atoms composing the cobalt
silicide film and the inter-hetero-atomic bond energy between said
adding element and Co atoms is close to the inter-iso-atomic atomic
bonde energy of the Co atoms.
Also, in case no adding element is contained in the region where
the difference between said inter-hetero-atomic bond energy and
inter-iso-atomic bond energy is less than about 20%, the ratio of D
to D.sub.0 sharply decreases from 1 to 0.7 and the effect of
inhibiting the grain boundary diffusion becomes conspicuous.
It was disclosed that nickel or iron element satisfies these
conditions and functions to inhibit the grain boundary diffusion of
Co atoms in the cobalt silicide film.
Referring to FIG. 16, it shows the influence of the adding element
concentration on grain boundary diffusion when nickel or iron
element is added 0 to 0.3 atomic % in the cobalt silicide film. It
is seen from FIG. 16 that when the adding element concentration is
about 0.05 atomic % or more based on Co in the cobalt silicide
film, the grain boundary diffusion coefficient decreases sharply to
inhibit diffusion. On the other hand, when the adding element is
added 50% or more, cobalt silicide becomes no longer able to exist
as such. Therefore, the ratio of the adding element to Co in the
cobalt silicide film is preferably 0.05 to 50 atomic %.
FIG. 17 shows the influence of the adding element concentration on
the grain boundary diffusion coefficient when nickel or iron
element is added 5 to 20 atomic % in the cobalt silicide film. As
is seen from FIG. 17, when the adding element concentration becomes
about 18 atomic % or more based on Co in the cobalt silicide film,
the grain boundary diffusion coefficient increases to reduce the
diffusion inhibitory effect. This is because the crystal structure
of cobalt silicide is deranged when the ratio of the adding element
becomes about 18 atomic % or more. Thus, the ratio of the adding
element to Co in the cobalt silicide film is preferably 0.05 to 18
atomic %.
For inhibiting the grain boundary diffusion, the adding element,
i.e. Ni or Fe atoms, may exist either in the form of silicide or as
a single body of Ni or Fe, but as shown in FIG. 3, the greatest
effect can be obtained when such an adding element 11 is segregated
at the crystal grain boundaries 8a in the cobalt silicide film
8.
As explained above, when a specific element--an element which has a
smaller atomic radius than the Co atoms composing the cobalt
silicide film and which meets the condition that the inter-atomic
energy between this element and Co element is not smaller or
greater than the inter-atomic energy of Co element by more than
20%--that is, nickel or iron element, is contained in the cobalt
silicide film, it is possible to inhibit the grain boundary
diffusion of Co in the cobalt silicide film, allowing inhibition of
coagulation of cobalt silicide to thereby prevent the rise of
resistance of said film.
In this embodiment of the invention, a cobalt silicide film is
formed on all of the gate electrode 4 and diffusion layers 5, 6,
but said film may be formed on the gate electrode or the diffusion
layers alone. Also, the diffusion layers 5, 6 may be of a LDD
structure. In either of these cases, the same effect can be
obtained.
The semiconductor device in this embodiment of the invention is not
restricted to the above-described construction, and the number of
the wiring layers is also not limited to one. Further, this
semiconductor device can be used for DRAM (dynamic random access
memory), SRAM (static random access memory), microcomputers, LSI
systems and such.
FIG. 4 shows a sectional structure of a principal part of a
semiconductor device in the second embodiment of the present
invention. In this figure, the parts corresponding to those in the
first embodiment are affixed the same reference numerals.
The semiconductor device according to the instant embodiment of the
present invention, as shown in FIG. 4, has MOS transistors 100
formed on the surface of a silicon substrate 1, each of said MOS
transistors comprising a gate oxide film 3, a gate electrode 4 made
of a polycrystalline silicone film, and a pair of diffusion layers
5, 6 (source and drain region). The respective MOS transistors are
isolated by an isolation film 2. Said gate electrode 4 is made of a
polycrystalline silicon film, a thin metal film, a metal silicide
film or a laminate thereof. Side walls 7 are formed on both sides
of said gate electrode 4. The gate oxide film 3 comprises, for
instance, a silicone oxide film, a silicon nitride film, a
ferroelectric film or a laminate thereof.
An insulating film 12 of the first layer is provided on the silicon
substrate having said MOS transistors formed thereon, and a cobalt
silicide film 26 is formed at the interface between the first layer
electric wiring 16 and diffusion layer 5 in a contact hole 13
formed in said first layer insulating film 12. Also, a
polycrystalline silicon plug 24 is embedded in another contact hole
formed in said first layer insulating film 12, and a cobalt
silicide film 25 is formed at the interface between the first layer
electric wiring 17 and said polycrystalline silicon plug 24.
Further, a cobalt silicide film 17 is formed at the interface
between said first layer electric wiring 17 and said gate electrode
4 in still another contact hole 15 formed in said first layer
insulating film 12.
Said cobalt silicide films 25, 26, 27 contain at least one adding
element 11, and at least one of such adding elements is nickel (Ni)
or iron (Fe). The Ni or Fe atoms in these cobalt silicide films may
exist either in the form of nickel or iron silicide or as a single
body of Ni or Fe.
Over the said first layer wirings 16, 17, 18 is provided an
insulating film 19 for electrically insulating the unit from the
outside. This insulating film 19 comprises, for instance, a BPSG
(boron-doped phosphosilicate glass) film, SOG (spin-on-glass) film
or a silicon oxide or nitride film formed by CVD or sputtering.
Thus, when an element which has a smaller atomic radius than the Co
or Si atoms and which is of such characteristics that the
inter-atomic energy between this element and Co atoms is not
smaller or greater than the inter-atomic energy of Co element by
more than 20%, that is, nickel or iron element, is contained in the
cobalt silicide film, it is possible to inhibit the grain boundary
diffusion of Co in the cobalt silicide film, thereby inhibiting
coagulation of cobalt silicide to prevent increase of resistance of
said film.
In this embodiment of the invention, the cobalt silicide films 25,
26, 27 containing nickel or iron as the adding element 11 are
formed on all of the diffusion layer 5, polycrystalline plug 24 and
gate electrode 4, but the cobalt silicide film may be formed on
only one of them. In this case, too, the same effect can be
obtained.
The semiconductor device in this embodiment of the invention is not
restricted to the above-described construction, and the number of
the diffusion layers is not limited to one. Also, this
semiconductor device may be used for DRAM (dynamic random access
memory), SRAM (static random access memory), microcomputers, LSI
systems, etc.
Next, the third embodiment of the present invention is described
with reference to FIG. 5.
FIG. 5 shows a sectional structure of a principal part of a
semiconductor device according to this embodiment of the invention,
in which the parts corresponding to those in the first embodiments
are affixed the same reference numerals.
The semiconductor device according to this embodiment shown in FIG.
5 is a modification of the semiconductor device according to the
first embodiment shown in FIG. 1. The difference of this embodiment
from the first embodiment is that in this embodiment a capacitor
101 comprising a laminate of a lower electrode 28, a dielectric
film 29 and an upper electrode 30 is provided on the insulating
film 12 of the first layer.
The dielectric film 29 constituting part of the capacitor is made
of, for instance, a silicon oxide film, a tantalum oxide film, a
BST (barium strontium titanate) film, a PZT (zinc zirconate
titanate) film or the like. The lower electrode 29 or upper
electrode 30 may be composed of, for instance, polycrystalline
silicon, titanium nitride, tungsten, ruthenium, indium, platinum,
ruthenium oxide, indium oxide or the like.
In the present embodiment of the invention, said cobalt silicide
films 8, 9, 10 contain at least one adding element 11, and at least
one of such adding elements 11 is nickel (Ni) or iron (Fe). The Ni
or Fe atoms in these cobalt silicide films may exist either in the
form of nickel or iron silicide or as a single body of Ni or
Fe.
It is thereby possible to inhibit the grain boundary diffusion of
Co in the cobalt silicide film, allowing inhibition of coagulation
of this film to prevent the rise of resistance of the film.
Now, the fourth embodiment of the present invention is described
with reference to FIG. 6.
FIG. 6 is a sectional structure of a principal part of a
semiconductor device according to the present embodiment, in which
the parts corresponding to those in the first or third embodiment
are affixed the same reference numerals.
The semiconductor device according to the present embodiment shown
in FIG. 6 is a modification of the semiconductor device according
to the first embodiment shown in FIG. 1 and that according to the
third embodiment. In the present embodiment, the semiconductor
device according to the first embodiment and that according to the
third embodiment are provided on a same silicon substrate 1. That
is, the semiconductor device according to the present embodiment is
of a structure in which memory unit 102 and CPU unit 103 are formed
on a silicon substrate 1.
In this embodiment, too, said cobalt silicide films 8, 9, 10
contain at least one adding element 11, and at least one of such
adding elements is nickel (Ni) or iron (Fe). The Ni or Fe atoms in
the cobalt silicide films may exist either in the form of nickel or
iron silicide or as a single body of Ni or Fe.
It is thereby possible to inhibit grain boundary diffusion of Co in
the cobalt silicide films, and accordingly coagulation is inhibited
to prevent the rise of resistance of the cobalt silicide films.
In the present embodiment, a cobalt silicide film is formed on all
of the gate electrodes 5 and diffusion layers 5,6 of both of the
memory unit 102 and CPU unit 103, but said film may be formed on
one of the memory unit 102 and CPU unit 103 or on the gate
electrodes or diffusion layers alone. Also, the diffusion layers 5,
6 may of a LDD structure. In this case, too, the same effect as
described above can be obtained.
Next, the process for producing a semiconductor device according to
the fifth embodiment of the present invention is described with
reference to FIGS. 7 to 10. An epitome of the production process in
the present embodiment is described stepwise in accordance with the
drawings.
FIG. 7: The principal surface of a silicon substrate 1 is sectioned
into an active region and an isolation region by an isolation film
2. A gate oxide film 3 and a gate electrode 4 are formed in the
active region of said silicon substrate 1. Then side walls 7 are
formed on both sides of said gate electrode 4. Then, with said gate
electrode 5, side walls 7 and isolation film 2 being masked,
impurities are injected into said silicon substrate 1 to form
diffusion layers 5, 6. This step is one which is commonly practiced
in the production of ordinary MOS transistors, and has no direct
bearing on the present invention. This step is not limited to the
above-described procedure but any ordinary transistor forming step
can be employed.
FIG. 8: An Ni-containing cobalt film 20 is formed in contact with
the upper side of at least said gate electrode 4 and diffusion
layers 5, 6 on said silicon substrate by, for instance, sputtering.
The Ni concentration in said Ni-containing cobalt film 20 is
preferably 0.05 to 50 atomic %, more preferably 0.05 to 18 atomic
%, based on Co. As for the method of forming said Ni-containing
cobalt film 20, a film is formed while mixing Ni and Co by using a
multi-stage sputtering device, or a film is formed by using a
target in which Ni and Co have already been mixed. Forming the film
while mixing Ni and Co by using a multi-stage sputtering device has
the advantage that there is no need of forming a specific target.
In case of forming the film by using a target in which Ni and Co
have already been mixed, there is the advantage that it is easy to
control the concentration of Ni relative to Co. Other methods than
sputtering, such as vacuum deposition can be used for forming the
film.
Then a titanium nitride film 21 is formed on said Ni-containing
cobalt film 20. The film formed on the Ni-containing cobalt film 20
may not necessarily be a titanium nitride film; it may be other
metal film or an insulating film, or such a film may not be formed
at all.
FIG. 9: Thereafter, a treatment, for instance, a 700.degree. C.
heat treatment is carried out to cause a silicide reaction of the
silicon of said gate electrode 4 and diffusion layers 5,6 with the
cobalt film, thereby forming the cobalt silicide films 8, 9, 10
selectively on said gate electrode 4 and/or diffusion layers 5, 6.
Here, Ni-containing cobalt silicide is formed by reacting silicon
with the Ni-containing cobalt film. Since the grain boundary
diffusion of Co atoms in the cobalt silicide film is inhibited,
there takes place no coagulation in the ensuing step of
high-temperature heat treatment, allowing formation of a
low-resistance cobalt silicide.
According to this production process, the principal surface of the
silicon substrate on which a cobalt silicide film is formed in
contact constitutes an Si (111) plane, and the principal surface of
cobalt silicide also forms a CoSi2 (111) plane as shown in FIG. 15.
This is for the reason that, because of use of an Ni-containing
cobalt film, the diffusion rate of Co atoms at the time of silicide
reaction of nickel is lowered, allowing the silicon-cobalt reaction
to take place slowly, so that cobalt silicide is formed in a most
stable state.
Then, the said unreacted Ni-containing cobalt film 20 and titanium
nitride film 21 on the isolation film 2 and side walls 7 are
removed by wet etching or other means.
In the above-described embodiment, a cobalt silicide film is formed
on both of the gate electrode a and the diffusion layers, but it
may be formed on only one of them.
Also, the heat treatment for forming the cobalt silicide film may
be carried out in two stages at about 500.degree. C. and about
700.degree. C., respectively. In this case, etching of the
unreacted Ni-containing cobalt film and titanium nitride film may
be conducted after 500.degree. C. annealing.
FIG. 10: Thereafter, other necessary steps are carried out to
complete a semiconductor device. For instance, an insulating film
12 of the first layer is formed in contact with the whole surface
of the silicon substrate including the cobalt silicide films 8, 9,
10, side walls 7 and isolation films 2, then contact holes 13, 14
are formed, followed by formation of electrical wirings 16, 17 of
the first layer, and finally an insulating film 19 is formed to
complete a semiconductor device.
The above-described step is but an exemplification and can be
replaced by other embodiments. Also, the number of the wiring
layers is not limited to one. In the present embodiment of the
invention, there was shown the production process of a
semiconductor device having the Ni-containing cobalt silicide
films. For producing a semiconductor device having the
Fe-containing cobalt silicide films, said Ni-containing cobalt film
20 is simply replaced by an Fe-containing cobalt film in the
above-described process.
This semiconductor device can be adapted to DRAM (dynamic random
access memory), SRAM (static random access memory), microcomputers,
LSI systems and such.
The production process of a semiconductor device according to the
sixth embodiment of the present invention is shown in FIGS. 12
through 15. An epitome of the production process according to this
embodiment is described stepwise in accordance with the
figures.
FIG. 12: An active region and an isolation region are provided on
the principal surface of a silicon substrate 1 by an isolation film
2. A gate oxide film 3 and a gate electrode 4 are formed in the
active region of said silicon substrate 1. Then, side walls 7 are
formed on both side of said gate electrode 4. Then, with said gate
electrode 4, side walls 7 and isolation film 2 being masked,
impurities are injected into said silicon substrate 1 to form
diffusion layers 5, 6. This step is one which is commonly practiced
in the production of ordinary MOS transistors, and has no direct
bearing on the present invention. This step is therefore not
limited to the above-described procedure but any ordinary
transistor forming step can be employed.
FIG. 13: A cobalt film 22 is formed, as by sputtering, in contact
with the upper side of at least said gate electrode 4 and diffusion
layers 5, 6 on said silicon substrate 1. On this cobalt film 22 is
formed a nickel film 23, on which a titanium nitride film 21 is
further formed. The film formed on said nickel film 23 may not
necessarily be a titanium nitride film; it may be other metal film
or an insulating film, or may not be provided at all.
FIG. 14: Thereafter, a treatment, for instance a 700.degree. C.
heat treatment is carried out to cause a silicide reaction of the
silicon of said gate electrode 4 and diffusion layers 5, 6 with the
cobalt film, thereby forming the cobalt silicide films 8, 9, 10
selectively on said gate electrode 4 and/or diffusion layers 5, 6.
Here, Ni-containing cobalt silicide is formed by reacting silicon
with the nickel-cobalt layered film. Since the grain boundary
diffusion of Co atoms in the cobalt silicide film is inhibited,
there takes place no coagulation in the ensuing step of
high-temperature heat treatment, allowing formation of a
low-resistance cobalt silicide.
The said unreacted Ni-containing cobalt film 22, nickel film 23 and
titanium nitride film 21 on the isolation film 2 and side walls 7
are removed by wet etching or other means.
In the above-described embodiment, a cobalt silicide film is formed
on both of the gate electrode and diffusion layers, but it may be
formed on only one of them.
Also, the heat treatment for forming the cobalt silicide film may
be carried out in two stages at about 500.degree. C. and about
700.degree. C., respectively. In this case, etching of the
unreacted Ni-containing cobalt film and titanium nitride film may
be conducted after 500.degree. C. annealing.
FIG. 15: Thereafter, other necessary steps are carried out to
complete a semiconductor device. For instance, an insulating film
12 of the first layer is formed in contact with the whole surface
of the silicon substrate including the cobalt silicide films 8, 9,
10, side walls 7 and isolation film 2, then contact holes 13, 14
are formed, followed by formation of electrical wirings 16, 17 of
the first layer, and finally an insulating film 19 is formed to
complete a semiconductor device. The above-described step is but an
exemplification and can be replaced by other embodiments. Also, the
number of the wiring layers is not limited to one.
In this embodiment of the invention, a cobalt film 22 is formed in
contact with the upper side of at least said gate electrode 4 and
diffusion layers 5, 6 on said silicon substrate 1, then an nickel
film is formed on said cobalt film 22, and then nickel silicide or
Ni-containing cobalt silicide is formed by a heat treatment, but
the order of lamination is of no account as far as a laminate of a
cobalt film and a nickel film is provided.
For instance, a nickel film 23 is formed in contact with the upper
side of at least said electrode 4 and diffusion layers 5, 6 on said
silicon substrate 1, then a cobalt film 22 is formed on said nickel
film 23, and then cobalt silicide is formed by a heat treatment. In
this case, too, the same effect as described above can be
obtained.
It is also possible to provide plural cobalt/nickel laminates. The
same effect can be obtained in this case, too.
In this embodiment, a process for producing a semiconductor device
having a cobalt silicide film containing Ni as adding element has
been described. For producing a semiconductor device having a
cobalt silicide film containing Fe as adding element, an Fe film is
used in place of the Ni film in the above process.
Also, this semiconductor device can be used for DRAM (dynamic
random access memory), SRAM (static random access memory),
microcomputers, LSI systems, etc.
According to the present invention, it is possible to inhibit grain
boundary diffusion of Co atoms in the cobalt silicide film by
containing in said film an element which has a smaller atomic
radius than Co atoms and which meets the requirement that the
inter-atomic energy between this element and Co element is not more
than 20% smaller or greater than the inter-atomic energy of Co
atoms, that is, nickel or iron element.
Therefore, it is possible to inhibit the Co atoms composing the
cobalt silicide film from being diffused along the crystal grain
boundaries, and to thereby inhibit coagulation of the film, in the
steps after formation of said film, even in case a high-temperature
heat treatment is conducted. Thus, there is provided a
semiconductor device having the cobalt silicide films which are low
in resistance even if reduced in thickness.
* * * * *
References